1. Field
The present invention relates to a wireless communication and, more particularly, to a method and apparatus for controlling downlink (DL) scheduling and Hybrid Automatic Repeat Request (HARQ) timing capable of being supported in a Time Division Duplex (TDD)-Frequency Division Duplex (FDD) joint operation.
2. Discussion of the Background
Automatic repeat request (ARQ) is one of the schemes that enhance reliability of a wireless communication. The ARQ refers to a scheme in which a transmitter retransmits a data signal if a data signal reception is failed at a receiver. Further, there is a scheme, hybrid automatic repeat request (HARQ), which is a combination of Forward Error Correction (FEC) and ARQ. A receiver that utilizes HARQ generally attempts an error correction for a received data signal and determines whether a retransmission needs to be performed by using an error detection code. As the error detection code, Cyclic Redundancy Check (CRC) scheme may be used. If data signal error is not detected from the detection process of CRC scheme, the receiver determines that a decoding process for the data signal is successful. In this case, the receiver transmits an Acknowledgement (ACK) signal to a transmitter. If data signal error is detected from the detection process of CRC scheme, the receiver determines that a decoding process for the data signal is not successful. In this case, the receiver transmits a Not-Acknowledgement (NACK) signal to a transmitter. If the transmitter receives the NACK signal, the transmitter may retransmit the data signal.
A wireless communication system may support Frequency Division Duplex (FDD) scheme and Time Division Duplex (TDD) scheme. In the FDD scheme, an uplink transmission and a downlink transmission may be simultaneously performed in a cell because a carrier frequency for an uplink (UL) transmission is different from a carrier frequency for a downlink (DL) transmission exists. In the TDD scheme, with respect to one cell, an uplink transmission and a downlink transmission are distinguished from each other based on different time slots. In the TDD scheme, a base station and a user equipment perform switching operations between a transmission mode and a reception mode because the same carrier is used for both an uplink transmission and a downlink transmission. In the TDD scheme, a Special Subframe may be added to provide a guard time for switching between the transmission mode and the reception mode. The Special Subframe may include Downlink Pilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time Slot (UpPTS). According to the TDD scheme, resource amounts for the uplink transmission and resource amounts for the downlink transmission may be asymmetrically assigned through various uplink (UL)-downlink (DL) configurations.
Currently, remaining frequency resources are scarce and various technologies have been utilized in wide frequency bands because of the frequency resource scarcity. For this reason, in order to provide a wideband bandwidth for supporting higher data-rate requirements, each of scattered bands has been configured to satisfy basic requirements to operate an independent system and a carrier aggregation (CA) scheme, which aggregates various frequency bands into one system, has been adopted. Here, each frequency band or carrier capable of an independent operation may be defined as a component carrier (CC). According to the adoption of the carrier aggregation system, ACK/NACK signals corresponding to a plurality of component carriers (CCs) need to be transmitted.
Recently, there is a need for a TDD-FDD joint operation scheme that supports a CA and/or a dual connectivity of an FDD band (or carrier) or a TDD band (or carrier). However, the standard only defines DL HARQ timing in relation to a FDD CA joint operation or a TDD CA joint operation, and it does not define the DL HARQ timing for the TDD-FDD joint operation. Therefore, there is a need for a method for configuring or controlling a new HARQ timing for the TDD-FDD joint operation.